It has heretofore been proposed to supply fuel to an internal combustion engine by means of a pressure-controlled electric-motor fuel pump and a one-way or non-return fuel line that connects the pump to a fuel rail and fuel injectors at the engine. A problem encountered with returnless fuel delivery systems of the described character is encountered during so-called hot soak conditions when the engine has been idling or running at low speed, especially during hot weather conditions, or when a hot engine is turned off. The high temperature of the fuel in the fuel rail, coupled with high ambient temperature conditions, causes the fuel trapped in the fuel rail to expand. Increased fuel pressure in the fuel rail helps prevent vaporization of fuel, which could otherwise result in vapor lock when the engine is restarted. However, when the engine is restarted, pressure in the fuel rail suddenly decreases, and can result in fuel vaporization, vapor lock and stalling of the engine. It is therefore important under such conditions to maintain high fuel pressure in the fuel rail after the engine has started and until the fuel has an opportunity to cool.
Parent application Ser. No. 181,848 discloses a returnless fuel delivery system for an internal combustion engine in which fuel under pressure is delivered by an electric-motor fuel pump through a fuel demand pressure regulator to the fuel rail and fuel injectors at the engine. Fuel is delivered to the demand regulator at substantially constant pressure (e.g., at 55 psig) by varying speed of the fuel pump as a function of fuel demand at the engine. The demand regulator has a housing with a flexible diaphragm that defines first and second chambers within the housing. Flow of fuel through the first chamber from the pump to the fuel rail (e.g., at 50 psig) is controlled by a valve coupled to the diaphragm. Under some operating conditions with the valve closed, fuel trapped between the valve and the fuel rail can expand and displace the diaphragm away from the valve so as to accommodate expansion of the fuel. In the preferred embodiments, the second chamber of the demand regulator is coupled to the engine air intake manifold so as to maintain substantially constant fuel pressure differential across the injectors under normal operating conditions. In one embodiment, a solenoid carried by the demand regulator housing is responsive to a temperature sensor at the fuel rail for opening the regulator valve and coupling the fuel rail directly to the fuel supply line so as to maintain elevated fuel pressure at the fuel rail and prevent fuel vaporization when temperature of fuel at the fuel rail increases to a preselected level (e.g., 170.degree. F.).
Although the fuel delivery system and fuel demand pressure regulator disclosed in the parent application address and overcome many difficulties theretofore extant in the art, further improvements remain desirable. In particular, the temperature sensor and solenoid valve disclosed in the parent application for opening the regulator valve when fuel temperature reaches a preselected level greatly increases the manufacturing cost of the demand pressure regulator and fuel delivery system. It is therefore a general object of the present invention to provide a fuel demand pressure regulator of the type disclosed in the above-noted parent application having facility for positioning the valve element in the open position, so as to couple the fuel supply line directly to the fuel rail and thereby maintain elevated pressure at the fuel rail to prevent fuel vaporization, when fuel temperature reaches a preselected level. Another and related object of the present invention is provide a demand pressure regulator and fuel delivery system of the described character that is less expensive to manufacture than heretofore proposed.